1. Field of the Invention
The present invention relates to a simple and economical method for drying a polyacrylamide gel which has undergone electrophoresis, while maintaining its transparency and without causing cracks.
2. Background Art
Polyacrylamide gels are very often used in electrophoresis analyses of biological macromolecules such as proteins and nucleic acid.
A polyacrylamide gel which has been used for performing electrophoresis of a biological sample and has been stained with a dye or the like cannot be stored for a prolonged period as it becomes brittle if left as is. Therefore, in many cases, profiles of electrophoresis are photographed or copied on paper or the like and stored as images.
However, photographing and copying involve difficulty in recording accurately thin bands or very subtle differences in density of stains. In addition, biological macromolecules which have been separated by electrophoresis cannot be recovered.
Therefore, it has been attempted to dry, for storage, a gel which has undergone electrophoresis, and a variety of methods have been proposed. For example, Japanese Patent Application Laid-open (kokai) No. 61-79151 discloses a method in which a heating plate provided exclusively for the purpose of drying is used and the gel is brought to dryness while being pressed against a support such as filter paper under reduced pressure. Japanese Patent Application Laid-open (kokai) No. 1-147356 discloses a method in which a gel is plasticized after being dewatered using an organic solvent. According to another method, a gel is sandwiched between semipermeable transparent films such as cellophane film before drying.
However, a method in which gels are dried with heat under reduced pressure requires a dedicated drying apparatus and a vacuum pump, which are both relationely expensive. In addition, when gels contain acrylamides at high concentrations of not less than 15% by weight, it often happens that gels are damaged due to cracking. In a method in which gels are dewatered using an organic solvent, gels tend to lose transparency or to deform, raising a problem in recording images accurately.
Compared to the above methods, a method in which gels are dried after being sandwiched between cellophane films or the like (hereinafter referred to as a cellophane sandwich method) is advantageous because it does not require special apparatuses. Moreover, it suppresses deformation of a gel during the drying process. Briefly, in this cellophane sandwich method, a gel is sandwiched between two films such as cellophane films or between a film such as cellophane and a plastic sheet, and the gel is dried while being pressed, making use of accompanying shrinking force of the films in the course of drying.
However, previous cellophane sandwich methods have a drawback similar to that involved in the above mentioned method involving heating under reduced pressure. That is, especially when using gels containing polyacrylamides at high concentrations of not less than 15% by weight, gels tend to generate cracks, thus impairing accurate recording of invaluable results of electrophoresis.
To avoid this problem, a number of methods have been proposed including incorporation of glycerol in a gel and application of gelatin or a paste onto the surface of a gel. However, any methods have turned out to be still uneffective for preventing the occurrence of cracks in the case of using gels having high concentrations of acrylamide.
Under the above circumstances, the present inventors conducted extensive studies and found that a polyacrylamide gel containing an acrylamide at a high concentration can be dried in a good state without causing cracks, if a polyacrylamide gel which has undergone electrophoresis is immersed in a solution containing one or more substances selected from the group consisting of saccharides, sugar alcohols having 4 or more carbon atoms, and water-soluble polymers; thereby impregnating the gel therewith before the gel is sandwiched between semipermeable transparent films such as cellophane. The present invention was accomplished based on this finding.